1. Technical Field
The present invention relates to an image forming apparatus comprising an image carrier which carries a toner image and a cleaner which abuts on the surface of the image carrier and removes toner, and to an image forming method which such an apparatus performs.
2. Related Art
Among image forming apparatuses of the electrophotographic type is an apparatus which comprises a cleaning blade (hereinafter referred to simply as a “blade”) which removes toner remaining on an image carrier. In this type of apparatus, friction between the image carrier and the cleaning blade may sometimes cause a problem that the image carrier gets worn away or that the edges of the blade curl up or get damaged. An approach for prevention of this is to always secure accumulation of toner in an abutting section where the image carrier and the blade abut on each other. In the image forming apparatus described in Japanese Patent No. 3026035 for instance, an output patch image is formed all along the width of a cleaning blade which abuts on a photosensitive member which serves as an image carrier, and the cleaning blade scrapes off the output patch. This prevents the blade from curling up at its edges.
According to the conventional technique described above, an output patch is formed all along the width of the cleaning blade, including the inside of an image region. This invites a problem that formation of the output patch uses a great amount of toner and the running cost of the apparatus accordingly increases. In addition, since it is not possible to form an image as is usually done while the output patch is being formed, another problem arises that the throughput of the apparatus decreases.
Further, among image forming apparatuses of this type is an apparatus which is structured to execute a control operation (registration control) which aims at properly maintaining a toner image forming position on an image carrier. The image forming apparatus described in Japanese Unexamined Patent Application No. 2001-235924 for instance performs registration control in the following manner, to thereby handle a slight change of the rotation speed of an intermediate transfer belt, namely, an image carrier, which occurs when a cleaning blade abuts on and moves away from the intermediate transfer belt. In this apparatus, while changing how the cleaning blade abuts on the intermediate transfer belt, the rotation cycle of the intermediate transfer belt is measured in each state. Describing this in more specific details, the rotation cycle of the intermediate transfer belt is measured in four situations that: (1) the intermediate transfer belt comes abutting on the intermediate transfer belt while the intermediate transfer belt makes one revolution; (2) the abutting state is maintained during a revolution; (3) the cleaning blade starts moving away from the intermediate transfer belt while the intermediate transfer belt makes one revolution; and (4) the cleaning blade stays away during a revolution.
A transfer position at which a toner image will be transferred onto the intermediate transfer belt is controlled based on the result of the measurement. In other words, for transfer of a toner image onto the intermediate transfer belt, whether the rotation of the intermediate transfer belt corresponds to any one of (1) through (4) is determined, and the transfer position is shifted by a registration control amount calculated from the corresponding measured rotation cycle.
In the conventional image forming apparatus described above, immediately after power-on of the apparatus, the cycle of the intermediate transfer belt described above is measured as a part of initialization of the apparatus before forming an image. However, a special consideration is necessary when the intermediate transfer belt is new which may be when the apparatus is new or immediately after the intermediate transfer belt has been exchanged. The reason is as follows.
It is known that when the image forming apparatus of this type is in its actual operation, a part of toner removed off from the intermediate transfer belt (image carrier) by the cleaning blade (cleaner) accumulates in the section where the blade and the belt abut on each other, and this toner functions as a lubricant between the cleaner and the image carrier and mitigates friction between the blade and the belt. On the other hand, when the apparatus is new, no such toner accumulation has been made yet. Hence, when the apparatus is new, if the image carrier rotates with the cleaner abutting on the same and the cycle of the image carrier is measured, friction may damage the cleaner or the image carrier. This also is the same as measurement of the cycle of the image carrier in a different condition from that under which the apparatus actually operates, which may end up in deteriorating the accuracy of registration control.
In addition, among image forming apparatuses of this type structured so as to be able to mount multiple developers which store toner is such an apparatus which a user can choose whether to use it as a color image forming apparatus or a monochrome image forming apparatus by deciding whether to mount developers for mutually different toner colors or developers for the same toner color, in order to meet diversified user demands (Japanese Unexamined Patent Application No. 2002-351190).
In the case of such an apparatus, the content of processing to be executed as initialization must become different depending upon whether the apparatus is used as a color image forming apparatus or a monochrome image forming apparatus. For example, measurement of the cycle of the intermediate transfer belt described above is required for accurately superimposing toner images one atop the other on the intermediate transfer belt but is not necessary for a monochrome image forming apparatus which due to its nature does not superimpose toner images. Initialization according to the conventional technique nevertheless provides no consideration on this, leaving a room for improvement with respect to the efficiency of initialization.